Variable inductance



March 1940- w. J. POLYDOROFF 2,192,519

I VARIABLE INDUCTANGE Original Filed Aug. 30, 1934 INVENTOR 144] P01 YfiO/POFF ATTORNEY Patented Mar; 5,

PATENT OFFICE VARIABLE INDUCTAN CE Wladimir J. Polydoroff, Wilmette, Ill., assignor to Johnson Laboratories, Inc., Chicago, Ill., a cornotation of Illinois Original application August 30,- 1934, Serial No. 742.026. Divided and this application June 3,

1937, Serial No. 146,238.

September 2, 1933.

8 Claims.

This invention relates to variable inductances, and more particularly to variable inductances suitable for use in high-frequency resonant circuits, arranged to be adjusted to any frequency within a relatively wide band. Variable inductances of this type may be employed, for example, in broadcast receivers. Y

The variable inductances of the present invention are of the type having compressed comminuted magnetic cores arranged to be movable relatively to the coils with which they are associated, the relative motion of the coil and core producing changes in inductance which permit tuning the resonant circuit of which the induct- 15 ance may form a part, with or without the usual capacitance variation.

Variable inductance devices suitable for tuning resonant circuits over a range having a ratio of maximum to minimum frequency of the order of 3 are disclosed in my French Patent No. 737,154. The present specification is addressed to cases in which it is desired to tune one or more resonant circuits through a plurality of frequency ranges which may be widely separated :25 from one another (e. g. the medium and long wavelength ranges usually provided for in modcrn broadcast receivers) and additionally to cases in which it is desired to tune over a range of frequencies greater in extent than can be covered 30 by a simple variable inductance device such as those described in my French patent above referred .to.

It is one object of the present invention, therefore, to provide variable inductance devices capable of being varied through two distinct ranges of inductance values. The maximum value of one range may be the same as the minimum value of the other, or they may be different. Another object of the invention is to operatively link at least two windings by a unitary common core structure in such a manner that the mutual inductance between two windings is considerably varied in addition to the usual inductance varia tion.

This application is a division of my United States Letters Patent No. 2,095,420 which issued on October 12, 1937, on improvements in Variable inductances' for tuned high-frequency circuits. The invention will be best understood by refer- 0 ence to the accompanying drawing, in which:

Fig. 1 shows an arrangement in which two coils are placed side by side with their axes parallel, and the relatively movable core member consists of two cylindrical portions, preferably joined by' a magnetic yoke;

In Great Britain Fig. 2 shows an arrangement in which the two coils are concentric, one coil being cylindrical and the other tapered in form, the core. member being shaped to adapt it to the coils; and

Fig. 3 shows an arrangement in which a cylin- 5 drical coil and a tapered coil are arranged side by side, the core consisting of separate members adapted to cooperate with the coils.

Magnetic core materials and cores suitable for use in the construction of the variable induct- 1o ances of the present invention are disclosed in my U, S. Patents Nos. 1,940,228 and 1,982,689.

In general, the cores consist of very finely divided magnetic material, such as pure iron, the particles being of such size as to reduce the losses in the resultant cores to a suitable minimum. The

particles are individually insulated with a suitable insulator and are then molded into compressed bodies of suitable shape by the employ ment of an appropriate plastic binding matego rial, sufficient pressure being used in the molding to give the resultant cores the desired value of apparent permeability.

Circuit arrangements in which variable in ductance devices of the types herein contem- '25 plated may be advantageously employed are described in my French Patents Nos. 737,154 and 771,898.

According to the present invention, two separate coils or windings are associated with a sin gle magnetic core unit, which is movable relatively to the coils. The movement may be so arranged that the core influences both coils simultaneously or it may be arranged in such a manner that the core influences either winding at will. In either arrangement the-inductances of the, two windings are controlled by the relative movement of the single core unit.

. In the embodiment shown in Flg. 1 the two coils or windings I, 2 are wound on two cylindrio cal forms 3, 4 of the same dimensions, although one coil may be of greater diameter than the other if required. In the arrangement shown in Fig. l the two coils l, 2 are mounted side by side with their axes parallel. The core member 6 5 consists of two cylindrical members 'I, 8 and a" yoke member 9. The coils I, 2 are securely supported by any suitable means and the core unit is arranged to be moved in such a manner that the core member I may be moved into and out 5 of coil I while the core member 8 moves into and out of coil 2. It will be understood that the two coils may be so connected relatively to each other that they will be either additive or subtractive in inductance value. As will be seen from the u in shape and is arranged to influence the induc- Additionally, the switching means may be arranged to connect the two coils in series or in parallel and to change the direction of the windings from an additive to a. subtractive relation or vice versa. By proper choice of the switching arrangement employed and by appropriate design of the coils themselves, variation of two or on a suitable support, such as a member ll consists of two plate. The core portions. l2 and I3.

the portion I: being of tubular form and 01'. such dimensions as Illa directly,

to influence the inductance of coil whereas the portion II is conical molded and mechanically joined in such a manner that they are intimately associated magnetically at one end, or the entire core member I I may be molded in one piece. The arrangement of this figure is particularly useful when the larger diameter winding Illa is used for shortwave tuning.

In the embodiment shown in Fig. 3, ,the coil i4 is cylindrical whereas the coil I! is conical in side with their axes parallel on any suitable support. The core member I8 is cylindrical in shape and is arranged to directly influence the inductance of the coil H. The core member I! consists of two portions IS, IS, the member l8 being conical in shape and adapted tosbe moved into the coil IS, the member ID beingtubular in shape and arranged to move outside the coil IS in such a manner as to substantially surround the coil 15 when fully advanced. The members l8 and I9 may be joined by of the internalcore member I 8 or a part or the external core member l9. Alternatively, the entirecore i1 consisting of the portions l8, I9, 20 may be molded in one piece. In Figs. 1 and 3 the smaller inductance coil alone operates over the high-frequency range, the other part of the core providing a low-reluctance path for the return flux, thus increasing the range. When the to increase the inductance variation.

In the arrangement of Figs. 1 and 3, the two coils (I, 2 in Fig.1 and I4, IS in Fig.3) are so connected that the fluxes in the two coils will be in opposite directions at any instant. Thus practically all the flux from one end of one coil enters the adjacent end of the other coil, the arrangement being what is commonly known as a binocular pair. It will be noted that the arrangement is such that current flow in one of shape, the two coils being mounted side by the windings is in opposite angular sense to current flow in the other winding. With the coils so wound and connected there is a very material increase in the coupling between the two coils if the core unit is advanced into them, because the core forms a substantially complete iron path for the flux. In this manner, a considerably greater variation in the inductance of the device with the twocoils connected in series and additively related, may be secured. v

It will be observed that the coils have been shown as single-layer solenoidal windings, since this produces minimum high-frequency resistance in the winding itself; but, where high inductance values are required, multiple-layer windings, preferably bank-wound, may be employed.

It is preferable to use a conductor consisting of several insulated strands, commonly known as Litz wire, for the windings, although, of course, a solid conductor may be used if desired. In practical embodiments of the invention it will frequently be found convenient to make one of the coils single-layer solenoidal with spaced turns for the higher frequency range, and the other coil a multiple-layer winding for the lower frequency range. I

For securing the relative movement between the coils and the core unit, any suitable mechanical drive. may be employed. Forms of mechanical movement which have been found to be suitable are described in my French Patent It will be understood that any of the arrange- 'ments herein described may be employed in the construction-of a band-pass filter or other tunoscillatory circuits are stood that plural inductance devices of types herein disclosed may be arranged to tune a plurality of circuits through two or more frequency ranges. 'In such embodiments the mechanical drive will move all the cores simultaneously, relatively to the coils, and adjustments such as those described in my French Patent No. 771,898 will be provided in order to secure and maintain synchronism or alignment of the several circuits.

Having thus described my invention, what I claim is:

1. A variable inductance device for multi-range tuning, including a compressed, comminuted magnetic core structure, two coaxial windings of different self-inductance value and of a type suitable for employment in the selective highfrequency circuits of radio receivers and whose effective inductance is varied by said core structure, and switching means to alter the connections of said windings, said core structure having an internal core portion and a concentric external shell portion and constituting a common magnetic path for said windings to increase the total effective inductance variation.

2. A variable inductance device for multi-range tuning, including a compressed comminuted magnetic core structure, two coaxial windings of diflerent self-inductance value and of a type suitable for employment in the selective highfrequency circuits of radio receivers and whose effective inductance is varied by said core structure, and switching means to alter the connections of said windings, said core structure having an internal core portion and a concentric exteru nal shell portion and constituting a common magnetic path for said windings to increase the total effective inductance variation, and being arranged to move into said two windings simultaneously.

3. A variable inductance device for multi-ran'ge tuning, including a compressed comminuted core structure having a yoke portion and two spaced portions projecting in the same direction from said yoke portion, two inductance coils for highfrequency tuning purposes operatively associated with said projecting core portions, said core structure and said coils being relatively movable for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting said coils in a desired circuit.

4. A variable inductance device for multi-range tuning, including a compressed comminuted core structure having a yoke portion and two spaced portions projecting in the same direction from said yoke portion, two inductance coils for highfrequency tuning purposes operatively associated with said projecting core portions, said core structure and said coils being relatively movable for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting one or both of said coils in a desired circuit.

5. A variable inductance device for multi-range.

tuning, including a compressed comminuted core structure having a yoke portion and two spaced portions projecting in the same direction from said yoke portion, two inductance coils for highfrequency tuning purposes operatively associated with said projecting core portions, said core structure and said coils being relatively movable 'for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting said coils in a desired circuit, said projecting core portions being concentric toreceive one of said coils between them, and the outer one of said core portions being in the magnetic path of the other of said coils.

. 6. A variable inductance device for multi-range tuning, including a compressed comminuted core inductance values, said structure having a yoke portion and two spaced portions projecting in the same direction from two inductance coils for highsaid yoke portion, frequency tuning purposes operatively associated with said projecting core portions, said core structure and said coils being relatively movable for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting one or both of said coils in a desired circuit, saidsprojecting core portions being concentric to receive one of said coils between them, and the outer-one of said core portions being in the magnetic path of the other of said coils. I

7. A variable inductance device for multi-range tuning, including a compressed comminuted core structure having a yoke portion and two spaced portions projecting in the same direction from said yoke portion, two inductance coils for high .frequency tuning purposes and of different selfinductance values, said coils being operatively associated with said projecting core portions, said core structure and said coils being relatively movable for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting said coils in a desired circuit, one of said projecting core portions constituting a common part of the magnetic paths of said two coils.

8. A variable inductance device for multi-range tuning, including a compressed comminuted core structure having a yoke portion and two spaced potions projecting in the same direction from sa d yoke portion, two inductance coils for highfrequency tuning purposes and of diflerent selfcoils being operatively associated with said projecting core portions, said core structure and said coils being relatively movable for tuning purposes, one of said projecting core portions being positioned and constituting a shield between said coils, and switching means for selectively connecting one or both of said coils in a desired circuit, one of said projecting core portions constituting a common part of themagnetic paths of said two coils.

wmnncra J. rombonor'r. 

